This invention relates to a ball spline assembly of the type in which angularly spaced rows of balls transmit torque between a splined shaft and an outer sleeve while reducing friction during relative axial movement of the shaft and the sleeve.
In a ball spline assembly of this type, the bore of the sleeve is formed with angularly spaced and axially extending grooves or raceways which receive the rows of balls. The shaft also includes ball-receiving grooves or raceways which are located between angularly spaced splines. The splines may be formed by moving a grinding wheel along a section of the length of the shaft in order to cut the raceways in the shaft. Near the end of the splined section, runout occurs where the grinding wheel makes less than a full depth cut as the wheel is retracted from the shaft. In the runout area, the depth of each raceway gradually decreases as the raceway progresses axially toward the non-splined section of the shaft.
A conventional ball spline assembly experiences problems when the shaft and the sleeve are at such an extreme relative axial position as to cause the balls to travel into the runout area of the shaft. As the balls encounter the shallow portions of the raceways in the runout area, the balls are forced radially outwardly until all radial clearance is removed from between the shaft, the balls and the sleeve. The resulting radial pressure can damage the components and can cause the assembly to lock.